Composite metal containing copper for coinage purposes



Sept. 9, 1969 p, s5 ET AL 3,466,157

COMPOSITE METAL CONTAINING COPPER FOR COINAGE PURPOSES Filed Oct. 22,1965 1N VENTORS PHIL/P B. NE/SSER MORRIS V. 80L E Y ATTORNEY UnitedStates Patent 3,466,157 COMPOSITE METAL CONTAINING COPPER FOR COINAGEPURPOSES Philip B. Neisser, Alexandria, Va., and Morris V. Boley,Bethesda, Md., assignors to the United States of America as representedby the Department of the Treasury Filed Oct. 22, 1965, Ser. No. 502,738Int. Cl. B23p 3/20 US. Cl. 29-499 13 Claims ABSTRACT OF THE DISCLOSUREThe present invention relates to a new composite metal strip havingouter layers of either copper-nickel or silvercopper alloys bondeddirectly to either a pure copper or silver-copper base, the layershaving appropriate alloy compositions and thicknesses to provide thecomposite strip with the necessary qualities of color, weight,brittleness, bounce, ring, electrical conductivity, magnetic attraction,and density to permit coinage which is compatible with present US.currency.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithont the payment of any royalties thereon or therefor.

This invention relates to composite or clad metals and, moreparticularly, to clad metals for use in the minting of coins.

In recent years the increasing rate of consumption of silver has becomea problem of major proportion. The amount of silver used for mintingcoins is increasing so rapidly that, along with the increasing demandfor industrial and space purposes, the supply of silver will soon not beadequate. As with the governments of many foreign countries, theGovernment of the United States has found it necessary to produce asubstitute for the silver coinage which has long been the traditionalform of currency.

The substitution of a silver-free alloy, or even an alloy containing asmaller percentage of silver, presents many complex problems. Any metalor alloy which is to be used for coinage must possess certainmechanical, chemical and physical properties as Well as meet thestringent test of public acceptability. In a mechanical sense the metalshould be sufficiently soft and ductile to be readily rolled, blankedand coined while, at the same time, be of adequate hardness to possessenough wear resistance after coining to permit a useful life in normalcirculation of 25 to 30 years.

Since coins which are in circulation over a period of years are exposedto many corrosive elements, the more obvious being, perspiration, softdrinks, salt spray and the like, and inasmuch as each of these elementsproduces a luster-dulling effect, it is important that any metal usedfor coinage possess high corrosion resistance. Additionally, toaccommodate for the possibility of a coin being swallowed oraccidentally coming in contact with food, the metal should beessentially nonreactive and nontoxic.

Of the necessary physical properties, electrical conductivity, magneticattraction and density are of prime importance, in that they directlyeffect the ability of coins to be accepted by coin-operated devices.That this requisite is of major importance is readily apparent When itis realized that the successful operation of nearly every coinop erateddevice, including vending machines, service-dispensing machines,toll-road collection boxes, pay telephones and amusement devices,depends upon these characteristics to operate the so-called coinselector mechaa ice nism. Although these mechanisms vary in degree ofsophistication, their purpose is to accept genuine United States coinsand reject all foreign coins, counterfeit coins, tokens and slugs. Thesecoin selectors or reject mechanisms not only examine the coins for size,weight, magnetic attraction and absence of a center hole, but also testthe resistivity-density product of the coin. This test, which is themost critical examination for genuine United States coinage, is based onthe well-known eddy-current principle and is feasible due to the factthat United States coins are nonmagnetic and have certain definite knownvalues of electrical resistivity and density.

Public acceptability, although of an indefinite and abstract nature, isrelated to a number of easily recognized factors. Experience withgenuine coins has enabled the public to distinguish genuine fromcounterfeit coins on the basis of such factors as color, weight,brittleness, bounce and ring. If any of these features are radicallychanged, it is quite likely that the coin would not be trusted and,accordingly, not accepted.

Accordingly, an object of the present invention is to provide acomposite or clad metal which fulfills all requirements necessary forUnited States coinage.

A further object of the invention is to provide a clad metal coin whichis substatnially equivalent to the customary United States silvercoinage in size, weight, color, bounce and ring.

Another object of the invention is to provide a clad metal coin having aresistivity-density product substantially equal to that of customaryUnited States silver coinage.

A still further object of the invention is to provide a method ofproducing a clad metal coin suitable for use as United States coinage.

A still further object of the invention is to provide a method ofproducing a coin which is substantially equivalent to the customaryUnited States silver coinage in size, weight, color, bounce, ring andresistivity-density product.

The exact nature of this invention, as well as other objects andadvantages thereof, will be readily apparent from consideration of thefollowing specification relating to the annexed drawing, in which:

FIG. 1 illustrates in a plan view a coin made in accordance with thepresent invention.

FIG. 2 shows a cross section taken along the line 2, 2 of FIG. 1 andillustrates one embodiment of the invention.

FIG. 3 illustrates another embodiment of FIG. 2.

FIG. 4 is a diagrammatic view of the eddy-current portion of the coinselector mechanism used in many coin-operated devices.

Referring now to the drawings, there follows a detailed description ofthe present invention. It has been discovered that a composite metalstrip can be produced which possesses substantially all thecharacteristics of customary United States silver coinage, including thestringent requirement of resistivity-density product. Two embodiments ofthe invention are shown by way of ex ample in FIGS. 2 and 3, wherein, inFIG. 2, a layer of copper 20 is clad on its upper and lower surfaceswith layers of cupronickel 22, and in FIG. 3 a silver-copper alloy 26 inWhich copper predominates is clad on its upper and lower surfaces bylayers of a silver-copper alloy 28 in which silver predominates.

The various embodiments of composite metals which may fall within theteachings of the present invention, including the embodimentsillustrated in FIGS. 2 and 3, may be clad by any of the many well-knownindustrial methods such as cold bonding, hot bonding, brazing orexplosive bonding.

The composite metal may be either originally clad to the desiredthickness or may be clad and subsequently rolled. After rolling, or iforiginally clad to the necessary thickness, the composite strip isprocessed through the blanking mechanism which punches the coin blanksor planchets. These planchets may then be annealed, if desired, orforwarded directly to the riddle for cleaning. The clean coin blanks orplanchets are then passed between rollers to raise or upset the rim ofthe blank. This operation is necessary in order to provide a rimthickness greater than that of any other portion of the coin to not onlyfacilitate stacking but also to provide better wear protection to thecentral portions of the coin. The upset blanks then proceed to thecoining operation wherein they are pressed simultaneously betweenobverse and reverse dies to form the complete coin design, including themilled edge or reeding.

Referring now to FIG. 4, a brief description of the eddycurrent coinselector mechanism will be set forth in order that the stringentrequirement of a specific resistivity-density product may be betterappreciated.

In the eddy-current mechanism illustrated in FIG. 4 an inclined track 30supported at its upper and lower ends by support members 32 has a magnet33 so arranged near is lower end to concentrate the magnetic lines offlux 36 perpendicular to the path of travel of coin 38 down the track30. In accordance with the well-known law of physics, as coin 38 travelsdown inclined track 30 cutting lines of flux 36 eddy currents aregenerated in coin 38 creating a magnetic field which impedes the motionof coin 38 through the primary magnetic field 36. As is well known, thedegree of retardation in the magnetic field is proportional to theproduct of the density and the electrical resistivity of the coin. Thecoin selector mechanisms presently in use throughout the United Statesaccept customary United States silver coinage (resistivitydensityproduct of 21.6 micro-ohm-grams per square centimeter) and reject purecopper (resistivity-density product 15.4) on the low side and 95copper-5 Zinc (resistivitydensity product of 27.0) on the high side. Thevarious embodiments of the present invention including the specificexamples hereinafter set forth have been found to haveresistivity-density products which lie within this acceptable range.

As specific examples of composite metals encompassed by the teachings ofthe present invention, the following exampes are given. They areillustrative only.

EXAMPLE 1 A clad strip suitable for minting coins in dime denominationsmay consist of a base or inner layer of pure copper having a thicknessof 021.001 inch and two outer layers composed of 7512.5% copper and2512.5% nickel, each having a thickness of 0071001 inch, the totalthickness of the strip being 0411.001 inch.

EXAMPLE 2 A clad strip suitable for minting coins in quarter dollardenominations may consist of a base or inner layer of pure copper havinga thickness of 0361001 inch and two outer layers composed of 7512.5%copper and 2512.5% nickel, each having a thickness of 0091001, the totalthickness of the strip being 0541.001 inch.

EXAMPLE 3 A clad strip suitable for minting coins in half dollardenominations may consist of a base or inner layer composed of 21.51.6%silver and 78.51.6% copper having a thickness of 0461002 inch and twoouter layers composed of 801.6% silver and 201.6% copper having athickness of 0101001 inch, the total thickness of the strip being0661.001 inch.

It is to be noted that the amount of silver could vary from between 75%to 85% in the outer layers and from between 20% to 25% in the innerlayer.

In addition to the many advantages already set forth there existnumerous other advantages inherent in the composite metals of the typeencompassed in the present invention, some of which will now bedescribed. Trial blanking operations on the illustrated embodiments ofthe invention have shown that as with the present United States coinagethe strip may be blanked in a cold-rolled condition resulting inplanchets having clean and sharp sheared edges. If annealing beforeblanking was required, as is the case with many other suggestedsubstitutes, the punch drags the metal leaving unsatisfactory burrededges.

The inevitable result of punching circular blanks from strip stock isthe relatively large percentage of scrap remaining as a skeleton afterthe coin blanks have been punched. In actual practice the remainingscrap amounts to approximately 30% of the original strip. With thecomposites of the present invention this scrap can readily be reverteddirectly into the melting cycle. Scrap from the cupronickel-coppercombination, since it consists only of copper and nickel, can beutilized in the production of additional cupronickel simply by addingproportionately more nickel to the charge in the melting furnace. Asimilar result is possible with the silver-copper scrap by addingcorrect amounts of silver or copper.

Other unique features of the present invention are difficulty ofcounterfeiting, wear resistance superior to that of present silvercoinage, and low cost.

As many changes could be made in the above composites without departingfrom the scope of the invention, it is intended that all mattercontained in the above description shall be interpreted as illustrativeand not in a limiting sense.

We claim:

1. In a coin a clad metal comprising a base layer of pure copper havinga thickness of 0271001 inch and two outer layers composed of 7512.5copper and 2512.5 nickel, each having a thickness of 0071.001 inch, thetotal thickness of the strip being 0411.001 inch.

2. In a coin a clad metal comprising a base layer of pure copper havinga thickness of 0361.001 inch and two outer layers composed of 7512.5%copper and 2512.5 nickel, each having a thickness of 0091001, the totalthickness of the strip being .0541001 inch.

3. In a coin a clad metal comprising a base layer composed of 21.51.6%silver and 78.51.6% copper having a thickness of 0461002 inch and twoouter layers composed of 801.6% silver and 201.6% copper, having athickness of 0101001 inch, the total thickness of the strip being0661.001 inch.

4. A composite metal comprising two cupronickel layers, an intermediatelayer of copper, said layers being bonded together, the cupronickellayers consisting of about 25% nickel, the relative thicknesses of thelayers being such that the resistivity-density product of the compositemetal lies in the range of 15.4 to 27.0 micro-ohmgrams per squarecentimeter.

5. In a coin a composite planchet comprising two cupronickel layers, anintermediate layer of copper, said layers being bonded together, thecupronickel layers consisting of about 25 nickel, the relativethicknesses of the layers being such that the resistivity-densityproduct of the planchet lies in the range of 15.4 to 27.0 microohm-gramsper square centimeter.

6. A composite metal having a sandwich structure, the outer layers beingof substantially equal thickness and being made of a cupronickel alloyconsisting essentially of about 25 nickel, an inner layer of highconductivity copper comprising about 50% to of the resulting metalthickness, said metal being characterized by a resistivity-densityproduct which lies in the range of 15.4 to 27.0 micro-ohm-grams persquare centimeter.

7. In a coin a composite planchet comprising a sandwich structure,having outer layers being of substantially equal thickness and made of acupronickel alloy consisting essentially of about 25 nickel, and aninner layer of high conductivity copper comprising about 50% to 90% ofthe total metal thickness, said planchet being characterized by aresistivity-density product which lies in the range of 15.4 to 27.0micro-ohm-grams per square centimeter.

8. A clad metal comprising two silver-copper outer layers consistingessentially of about 75 to 85% silver, an intermediate silver-copperlayer consisting essentially of about 20% to 25% silver, said layersbeing bonded together, the relative thickness of the layers being suchthat the resistivity-density product lies in the range of 15.4 to 27.01nicro-ohm-grams per square centimeter.

9. A clad metal comprising two silver-copper layers consistingessentially of about 80% silver, an intermediate silver-copper layerconsisting essentially of about 20% silver, said layers being bondedtogether, the relative thickness of the layers being such that theresistivity-density product lies in the range of 15.4 to 27.0micro-ohmgrams per square centimeter.

10. In a coin a composite planchet comprising two silver-copper outerlayers consisting essentially of about 75% to 85% silver, anintermediate silver-copper layer consisting essentially of about 20% to25% silver, said layers being bonded together, the relative thickness ofthe layers being such that the resistivity-density product lies in therange of 15.4 to 27.0 micro-ohm-grarns per square centimeter.

11. In a coin a composite planchet comprising two silver-copper layersconsisting essentially of about 80% silver, an intermediatesilver-copper layer consisting essentially of about 20% silver, saidlayers being bonded together, the relative thickness of the layers beingsuch that the resistivity-density product lies in the range of 15.4 to27.0 micro-ohm-grams per square centimeter.

12. A clad metal having a sandwich structure, the two outer layers beingof substantially equal thickness and being made of a silver-copper alloyconsisting essentially of about 75% to 85% silver, an intermediatesilver-copper alloy layer consisting essentially of about 20% to 25%silver, the intermediate layer comprising about to 90% of the metalthickness, the relative thickness of the layers being such that theresistivity-density product lies in the range of 15.4 to 27.0micro-ohm-grams per square centimeter.

13. In a coin a composite planchet having a sandwich structure, twoouter layers being of substantially equal thickness and made of asilver-copper alloy consisting essentially of about to silver, anintermediate silver-copper alloy layer consisting essentially of about20% to 25 silver, the intermediate layer comprising about 50% to %of theplanchet thickness, the relative thickness of the layers being such thatthe resistivitydensity product lies in the range of 15.4 to 27.0microohm-grams per square centimeter.

References Cited UNITED STATES PATENTS 2,094,482 9/1937 Weder 29-1993,407,050 10/1968 Trapp 29-199 1,077,977 11/1913 Fuller 29196.3

2,445,858 7/1948 Mitchell 29199 2,646,616 7/1953 Davignon 29-1992,772,963 12/1956 Pease 29199 XR HYLAND BIZOT, Primary Examiner

